Sacrificial anode



July 14, 1953 R. D. TAYLOR SACRIFICIAL ANODE Filed June 15, 195o /JTEFL P/Pf INVENTOR. 'd/[ j Yay/0f BY Y #fr0/mfr m All Patented July 14, 1953 SACRIFICIAL ODE RichardV D. Taylor, Suffern, N. Y., assignor to American Smelting and Refining Company, H New York, N. Y., a corporation of New Jersey- Application JuneV 15, 1950, Serial No. 168,280

Claims.

This invention relates to an improved sacri-v ficial anode for the cathodic protection of metals against corrosion and, more particularly, to an improved core for use in such an anode.

Expendable metal anodes, usually of magnesium or Zinc or an alloy thereof, are widely used for the protection of metal pipelines and other underground metal structures and also for the protection of ships and submerged metal structures against corrosion. In such service the sacrificial anode is placed underground or in the medium causing the corrosion and is connected electricallyl to the Vstructure to be protected. Since the anode is electronegative with respect to the structure to be protected it is preferentially dissolved thereby preserving the structure. Electrical connection with the anode is usually made by means of an ironpipe Aor rod, called the core, irri-bedded in the anode. However, this mode of construction is not entirely satisfactory because the pipe or rod does not make good electrical connection with the anodic metal and the bond between core and metal lacks mechanical strength. In fact, anodes of this type have been found in which the pipe or rod would readily pull out of the metal of the anode and in some cases the union is so poor that the anode fails to function at all or in the Words of the art-goes dead after only a short period of service. It is thought that this defect is caused in part by poor bonding of the core to the anode material and perhaps to a larger extent by corrosion of the core through seepage of water or corrosive liquids along the pipe or rod from the top whereby the connection between the core and the metal of the anode is destroyed. In many installations such anodes are designed to protect structures for periods of as long as years. Thus it is particularly objectionable to have the anode go dead before its useful life is exhausted. Such a condition may endanger the structure being protected, and serve to increase the cost of use of such anodes.

Accordingly, it is an object of the invention to provide a sacrificial anode in which the core is firmly bonded to the metal of the anode.

Another object of the invention is to provide a sacrificial anode of longer service life than those heretofore used.

Still another object of the invention is to provide a sacrificial anode in which the core is firmly bonded to the anodic metal and is impervious to seepage of corrosive liquid between the core and anodic metal.

(Cl. .2M-197) A still further object is to provide an expendable anode in which the area of contact between the core'and anodic metal is substantially increased 'over 'that o'f the prior art.

Various other objects and advantages of the invention -will be apparent as the description proceeds.

' The invention will be explained with reference to the accompanying drawing, in which:

Fig. l is a vertical cross lsectional view of the improved anode with the' inner core partially in elevation with the anode shown schematically as connected to a steel pipeline to be protected.

Fig. 2 is ahorizontal section through the anode taken on a line 2 2 of Fig. 1.

Referring to the drawings, Fig. 1 shows an underground steel pipeline l protected by a sacriiicial magnesium anode 2 which is connected electrically to the steel pipe by a conductor 3. The core l of the anode, the lower portion of which is shown in vertical cross section and the upper portion in elevation, protrudes from the body of the anode into the cup-like depression 5 at the top yof the anode and is joined to the electric conductor 3 at 6. The joint and depression are sealed with a suitable insulating material '1. Reference character 8 indicates the manner in which the magnesium alloy penetrates the open space of the core during casting to yield a firm bond between the core and metal body of the anode.

The core 4 used in the improved anode is of iron strip, preferably galvanized, formed as an open pitch helix, i. e., an open, elongated spiral. A relatively thin strip of approximately 1%" in thickness is satisfactory although other thicknesses may be used. Molten anodic metal is cast around such a core in a suitable mold so that the metal flows readily into the openings in the open pitch of the helix making a firm bond both inside and out throughout the length of the open tube. Such bond or union has proved to be excellent from the standpoints both ol electrical conductivity and mechanical strength. The bond is so secure that seepage of corrosive liquids between core and anodic metal into the interior of the anode is prevented at the point of protrusion 9 of the core from the anode metal thereby preventing corrosion and weakening of the bond. This is a specic advantage of the improved anode over those of the prior art.

'Ihe open space in the helically wound strip as shown at l0 may be varied within reasonable limits as long as complete penetration of metal into the open tube is secured in the casting process.

As the anodic metal 2, magnesium or an alloy principally of such metal is useful. For example, a magnesium-base alloy of the following percentage composition was found to be effective: A1 5-7%, Zn 2-4%, Mn 0.10% min., Cu 0.1% max., Fe 0.003% max., Ni 0.003% max., Si 0.35% max. and minor constituents 0.3% maX.

Other alloys of magnesium are of course operative but it is preferred to use an alloy as low in iron and nickel content as is practicable. For certain uses, special high grade zinc is useful as the anodic metal.

The anodic metal may 'be cast around the open pitch helix in any convenient shape and in any size deemed desirable.

The improved anode may be used to protect a great variety of underground metal structures,

or metal structures immersed 'in water which are cathodic w-i-th respect to ymagnesium ior its alloys or high purity zinc.

While the invention has been particularly described With reference to a certain shape of anode and a specic kind 'of open pitched helical strip iron core in -the protection of iron pipe, it will be apparent to those skilled in the art that the invention is not limited to the -specific -core or shape of anode shown or to the particular alloy described but may be `modified in various manners Within the scope of the appendedclaims.

What is claimed is:

1. A sacricial meta-1 anode vcomprising a metal core embedded in a 4body of ananodic protective metal and disposed centrally therein and bonded thereto, said core rcomprising .a rigid,- self-sus taining, open pitch .helix v'of strip metal in the form of a hollow tube-'likefshape having an arcuate transverse cross-,sectional area, said strip 4 metal also being of uniform thickness throughout its length.

2. An anode according to claim 1 wherein the anodic protective metal is composed of high purity zinc.

`uniform thickness throughout its entire length.

5. Asacriflcial metal anode comprisinga metal core embedded in a body of an anodic protective metal and disposed centrally therein and bonded thereto, said protective metal being composed principally .of Zinc, said core kcomprising a rigid. self-sustaining, open pitch helix of galvanized iron .strip metal in the form of a hollow tubelike :shape having an arcuate transverse crosssectional area, said strip metal being of uniform thickness throughout its entire length.

RICHARD D. TAYLOR.

References Cited in the file of this patent FOREIGN PATENTSl Country o 'Date Great Britain of 1838 OTHER REFERENCES Corrosionf vol. 1, No. 2, June 1945, pages 63-66.

Number 

1. A SACRIFICIAL METAL ANODE COMPRISING A METAL CORE EMBEDDED IN A BODY OF AN ANODIC PROTECTIVE METAL AND DISPOSED CENTRALLY THEREIN AND BONDED THERETO, SAID CORE COMPRISING A RIGID, SELF-SUSTAINING, OPEN PITCH HELIX OF STRIP METAL IN THE FORM OF A HOLLOW TUBE-LIKE SHAPE HAVING AN ARCUATE TRANSVERSE CROSS-SECTIONAL AREA, SAID STRIP METAL ALSO BEING OF UNIFORM THICKNESS THROUGHOUT ITS LENGTH. 